Programmable resistive memory devices are being considered for data storage. One type of programmable resistive memory device is a programmable metallization cell (PMC). A first logic value may be written to a programmable metallization cell memory device by setting the device to a low resistance state, and a second logic value may be written by setting the device to a high resistance state. The logic value stored in the device may be read by sensing device resistance.
Consider a programmable metallization cell including first and second conductors separated by a silver-rich dielectric. Unprogrammed, the programmable metallization cell has a high resistance between its conductors. However, when an appropriate voltage is applied across the conductors, a conductive filament begins to form between the conductors. Once the filament bridges the conductors, the resistance of the programmable metallization cell is reduced substantially. The programmable metallization cell may be restored to its original (higher) resistance state by reversing the voltage over time.
Random access memory (RAM) that is based on PMCs would have lower power consumption than short-term memory such as DRAM, SRAM and Flash memory, and it would perform read and write operations much faster (by orders of magnitude) than conventional long-term storage devices such as hard drives. PMC-based RAM would be more compact and consume less power than typical hard drives.
During the lifetime of PMC-based RAM, many write operations would be performed on each PMC memory device. Consequently, each PMC memory device would cycle between resistance states many times.
However, repeated cycles can be a problem for PMC-based RAM. PMC memory devices have limited “endurance.” After a number of cycles, a PMC memory device cannot be restored to its original resistance state. Once this happens, the PMC memory device becomes unusable.
Error code correction could be used to recover data from an unusable memory device. However, if a large number of memory devices fail, the error code correction becomes costly, both from a time standpoint and a computational standpoint. If a large number of PMC memory devices fail, the PMC-based RAM can become unusable.
It would be desirable to increase the endurance of PMC memory devices.